Lars likelier to become someone who murders several people over a period (6,6)
I believe the answer is:
serial killer
'someone who murders several people over a period' is the definition.
'serial killer' can be an answer for 'someone' (serial killer is a kind of someone). I am not sure about the remainder of the definition.
'lars likelier to become' is the wordplay.
'to become' indicates an anagram.
'lars'+'likelier'='larslikelier'
'larslikelier' anagrammed gives 'SERIAL KILLER'.
Can you help me to learn more?
(Other definitions for serial killer that I've seen before include "One perpetrating many murders at different times" , "One carrying out a run of murders" , "Regular butcher" , "Mass murderer" .)